I have a new problem here. I'm still learning C for PIC (xc8 compiler) and as a beginner project i'm doing a thermometer with the popular ds18b20 and a pic16f628 i had lying around. My program does behave good when it is allowed to run but while i was playing with pointers, structures, arrays etc. to return more than one value in a function i noticed something went haywire and now the PC goes back and forth not allowing the program to run sequentially, at least that's what i see if I use the simulator in mplabx. I'm quite sure I have forgot something about program and/or memory locations but i can't figure out what or why. Can someone help me? I paste here the main code, what else do you need?
/*
* File: termometro.c
* Author: zakkos
* Created on April 18, 2013, 2:20 PM
*
* /
/*ESSENTIAL DEFINITIONS*/
#define _XTAL_FREQ 4000000
/*INCLUSIONS*/
#include <xc.h>
#include <stdio.h>
#include <stdlib.h>
#include <lcd.h>
#include <1-wire.h>
/*CONFIG PRAGMA*/
#pragma config BOREN = OFF, CPD = OFF, FOSC = INTOSCIO, MCLRE = OFF, WDTE = OFF, CP = OFF, LVP = OFF, PWRTE = ON
//typedef unsigned char uint8_t;
void read_temp(void);
union {
char eratura;
char decimali;
}temps;
int main(void) {
INTCON = 0x00;
PIE1 = 0x00;
CMCON = 0x07; //disabilito i comparatori - disable comparators
TRISA = 0x00;
PORTA = 0x00;
TRISB = 0x00;
PORTB = 0x00;
const char decims[16] = {0, 0, 1, 1, 2, 3, 3, 4, 5, 5, 6, 6, 7, 8, 8, 9};
char temp;
lcd_init();
lcd_send_cmd(LCD_CLR);
lcd_send_cmd(LCD_HOME);
writeString("Hello,");
lcd_send_cmd(LCD_LN2);
writeString("World!");
__delay_ms(1000);
while(1)
{
read_temp();
lcd_send_cmd(LCD_CLR);
lcd_send_cmd(LCD_HOME);
writeString("Temp:");
lcd_send_cmd(LCD_LN2);
if((temps.eratura & 0x80)){ //if sign bit is set
temps.eratura = ~temps.eratura; //2's complement
temps.eratura += 1;
temps.decimali = ~temps.decimali; //2's complement
temps.decimali += 1;
lcd_send_dat(0x2D); //minus
}
temp = (temps.eratura/100)& 0x0F; //centinaia 157/100=1 (hundreds)
if(temp){
lcd_send_dat(0x30 | temp);
temp = ((temps.eratura/10)%10) & 0x0F; //decine 157/10=15%10=5 (tens if hundreds is set, meaning it will display also a 0)
lcd_send_dat(0x30 | temp);
} else {
temp = ((temps.eratura/10)%10) & 0x0F; //decine 157/10=15%10=5 (tens if hundreds is no set, meaning it will not display if 0)
if(temp){lcd_send_dat(0x30 | temp);
}
}
lcd_send_dat(0x30 | (temps.eratura%10)& 0x0F); //unita 157%10=7 (ones)
lcd_send_dat(0x2E); //dot
lcd_send_dat(0x30 | decims[temps.decimali] & 0x0F); //decimals
lcd_send_dat(0xDF); //degrees
}
}
void read_temp(void){
char scratchpad[9];
while(ow_reset());
ow_write_byte(0xCC);
ow_write_byte(0x44);
while(ow_read_bit()==0);
__delay_ms(1);
while(ow_reset());
ow_write_byte(0xCC);
ow_write_byte(0xBE);
for(char k=0;k<10;k++){
scratchpad[k] = ow_read_byte();
}
temps.decimali = scratchpad[0] & 0x0F;
temps.eratura = (scratchpad[1] << 4)|(scratchpad[0] >> 4);
return;
}
On the microchip forum they spotted a flaw in the code. Turns out the problem was me, I didn't account for a negative index in the decims[]; array when it was evaluated in the case of a negative temperature
if(temps.eratura < 0){
temps.eratura = -temps.eratura;
temps.decimali = -temps.decimali;
lcd_send_dat('-');
}
then used in
lcd_send_dat(decims[temps.decimali]); //decimals
the 2's complement of a byte containing only the lower nibble (0x0F) has the most significant nibble set (0xF1). This was the source of all my problems! Adding a mask on the lower nibble after complementing the byte solved the problem:
if(temps.eratura < 0){
temps.eratura = -temps.eratura;
temps.decimali = -temps.decimali & 0x0F;
lcd_send_dat('-');
}
Thank you all for the answers, you really helped me a lot in understanding how things work!